Hi Richard,
If you are fresh to boat modelling then a tug would probably be the most practical subject for a working model.
You might want to consider starting off with a kit to get your hand in, so to speak, in which case something like the Wyeforce or Al Khubar from The Model Slipway would be a good choice. Model Slipway kits go together very well and are a good introduction to model boating.
http://www.modelslipway.com/
If you prefer a more traditional looking tug then Jotika's Joffre might fit the bill.
http://www.jotika-ltd.com/Pages/1024768/Ccraft_Front.htm
MyHobbyStore do have a number of plans in their Plans Service range but in many cases you will not get a great deal of constructional detail so you will have to be able to interpret the plan and read up on building techniques beforehand. There are several books available.
http://www.myhobbystore.co.uk/browser/119/tug
No doubt others will also have some suggestions for you.
I think the most important thing is not to be to ambitious to start with as this can often lead to disappointment.
Regards,
Colin